Multi-fit cap

ABSTRACT

A screw cap for sealing containers with threaded necks includes an outer body, having a cylindrical outer wall closed at one end by a circular lid and an interior neck seal adjacent to the circular lid. A female thread extends around an inner surface of the cylindrical outer wall. The female thread has a main portion having substantially uniform thickness, and an attachment portion having a thickness which is less than the thickness of the main portion. The female thread is attached to the inner surface of the cylindrical outer wall in the region of the attachment portion, and the attachment portion is configured to permit deflection of the female thread.

TECHNICAL FIELD

This invention relates to screw caps for sealing plastic containers.

BACKGROUND

Plastic jug bottles are used for the transportation of a variety ofliquids, both hazardous and non-hazardous. Such bottles are available ina range of capacities, typically from 1 litre to 20 litres.

Plastic jug bottles are typically sealed by screw caps. A female threadinside the cap engages with a male thread around the neck of the bottleto tighten the cap onto the bottle neck. The mouth of the bottle pressesagainst a layer of sealing material or a neck seal within the cap as itis tightened, sealing the contents of the bottle. A close fit betweenthe male and female threads helps to ensure the cap can be sufficientlytightened to create a secure seal and prevent leaking. A tight seal isparticularly important for bottles containing hazardous products.

The diameters of the bottle neck and the male thread of standard plasticjug bottles can vary by up to 5% of their nominal diameters betweendifferent manufacturers. This variation in dimensions can have adetrimental effect on the engagement of the male thread of the bottlewith the female thread of the cap, preventing the cap from tighteningproperly and compromising the integrity of the seal when closed. Bottlesfrom one manufacturer therefore have to be matched with caps from adesignated manufacturer to ensure proper engagement of the threads.

The present invention seeks to provide a solution for allowing one capof nominal size to fit a variety of container necks.

SUMMARY OF INVENTION

According to the present invention, there is provided a screw cap forsealing a container with a threaded neck, the screw cap comprising: anouter body, comprising a cylindrical outer wall closed at one end by acircular lid and an interior neck seal; and a female thread extendingaround an inner surface of the cylindrical outer wall. The female threadcomprises a main portion having a substantially uniform thickness and anattachment portion having a thickness which is less than the thicknessof the main portion. The female thread is attached to the inner surfaceof the cylindrical outer wall in the region of the attachment portion,and the attachment portion is configured to permit deflection of thefemale thread.

The attachment portion is located adjacent to the inner surface of theouter cylindrical wall. The reduced thickness of the attachment portionallows the thread to deflect when a force is applied to it, for examplewhen the cap is screwed onto a bottle neck. Deflection of the femalethread as it interconnects with the male thread of the bottle neckadvantageously permits the end portion to align with and fully engagebetween the ridges of the male thread, without requiring accuratematching of the cap to the dimensions of the neck bottle, ensuring atight seal when the cap is completely closed.

The term “thickness” is intended to have its usual meaning in thiscontext, i.e. the thickness of the main portion is the minimum distancebetween the lower surface and the upper surface of the main portion atany given point. Similarly, the thickness of the attachment portion isthe minimum distance between the lower surface and the upper surface ofthe attachment portion. It will be understood, however, that althoughthe thickness of the main portion is substantially uniform along itslength, the free end of the female thread may have a slightly reducedthickness due, for example, to rounding of the corners.

It will also be understood that the total length of the female thread isthe distance to which the female thread extends away from the outer wallof the cap, measured in a direction perpendicular to the outer wall. Thelength of the attachment portion is the distance between the outer walland the main portion of the female thread, i.e. the point at which thethickness of the female thread is no longer reduced.

The screw cap may be formed of a moulded polymer material. The mouldedpolymer material may comprise one or more of the following: high densitypolyethylene (HDPE), low density polyethylene (LDPE), polyacetal,polyamide, or any suitable rigid polymer. In an embodiment, the mouldedpolymer material is HDPE, nylon, or a combination thereof. The mouldedpolymer material may be selected based on a number of characteristics,such as: elasticity, which permits the thread to deflect while inengagement with the bottle neck but return to its original configurationwhen removed from engagement; rigidity and durability, to preventdeformation or breakage; and compatibility with the contents of thecontainer which the cap is intended to seal. The skilled person willunderstand that the moulded polymer material is not limited to theseexamples, and that any material suitable for moulding and having thenecessary durability may be used.

The moulded polymer material may be selected to work in conjunction withthe attachment portion, to permit deflection of the thread while alsopreventing breakage of this portion, which might otherwise be weakeneddue to its reduced thickness. The attachment portion may be subjected toa significant amount of strain when the cap is screwed onto the bottleneck, due to a combination of deflection and rotational force. Thepolymer must therefore be resilient and durable to withstand thisstrain, but also flexible enough to allow the thread to deflect andperform its function. For example, HDPE or polyamide may exhibitsuitable resilience and flexibility for this purpose.

The outer body of the cap, the female thread and the neck seal may eachbe formed of a different material, where necessary to achieve thedesired physical characteristics of each component. For example, theouter body may be formed of a more rigid material, whereas the femalethread may be formed of a more flexible material.

In an embodiment, the neck seal is formed from a softer material thanthe outer body. In an embodiment, the neck seal consists of a thin layerof material, such as a polytetrafluoroethylene (PTFE) liner. The neckseal may be formed from a material that is resistant to corrosion andoxidation, or is specifically resistant to the chemicals which areintended to be contained within the bottle.

The attachment portion of the female thread has a thickness that is lessthan the thickness of the main portion. The thickness of the attachmentportion may be between 90% and 50%, between 80% and 60% or between 75%and 67% of the thickness of the main portion. The length of theattachment portion may be more than 5% and no more than 33%, or morethan 5% and no more than 20%, of the total length of the female thread.In an embodiment, the length of the attachment portion is between 10%and 15% of the total length of the female thread.

In an embodiment, the main portion comprises an inclined region, whichextends from the attachment portion in a direction away from the lid ofthe outer body, i.e. in a downward direction when the cap is uprightwith the lid at the top. The inclined region may extend from theattachment portion at an inclination angle of between 10° and 65°,between 20° and 55° or between 30° and 45°.

In an embodiment, the main portion further comprises an end portion,which extends from the inclined region at an angle such that the endportion is parallel to the lid of the outer body. The length of the endportion (i.e. the distance between the inclined region and the free endof the female thread) may be between 10% and 40%, or preferably between25% and 33% of the total length of the female thread.

When the cap is screwed onto a bottle neck, in use, the end portionremains substantially horizontal and is therefore able to fit betweenthe ridges of the male thread and engage correctly despite anydeflection of the female thread. This ensures that the cap can bescrewed on tightly to create a reliable seal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side perspective view of a typical jug bottle neck.

FIG. 2a is an external side view of a screw cap according to anembodiment of the present invention, in engagement with a bottle neck.

FIG. 2b is a schematic cross-sectional view through section A-A of FIG.2 a.

FIG. 3 is a schematic cross-sectional representation of the thread areaof a screw cap according to an embodiment of the present invention, inengagement with a bottle neck.

FIG. 4 is a detail of a cross-section of the thread area of the screwcap of FIG. 3, showing exemplary dimensions.

DETAILED DESCRIPTION

FIG. 1 shows a typical jug bottle neck 100 of diameter E. The neck has amale thread 102 of diameter T. Diameters E and T can vary by up to 5% oftheir nominal dimensions depending on the manufacturer.

FIG. 2a shows a screw cap 200 according to an embodiment of the presentinvention, in engagement with a bottle neck 100 such as the one shown inFIG. 1.

FIG. 2b shows a cross-sectional view through section A-A of FIG. 2a .The screw cap 200 comprises an outer body, which comprises a cylindricalouter wall 204 closed at one end by a circular top or lid 206, and afemale thread 208 extending around an inner surface 210 of thecylindrical outer wall 204. The female thread 208 is shown in engagementwith the male thread 102 of the bottle neck 100.

The female thread 208 comprises an attachment portion 212 and isattached to the inner surface 210 in the region of the attachmentportion 212. The female thread 208 further comprises a main portion,which consists of an inclined region 214, extending downwardly from theattachment portion 212 (i.e. away from the lid of the cap 206), and anend portion 216, extending from the inclined region 214 to the free end213 of the female thread 208. The end portion 216 extends from theinclined region 214 at an angle, so that it is approximately parallelwith the lid of the cap 206.

The attachment portion 212 has a reduced thickness compared with themain portion, which allows the female thread 208 to deflect as itinterconnects with the male thread 102 of the bottle neck 100. This inturn allows the end portion 216 to align with and fully engage betweenthe ridges of the male thread 102, without requiring accurate matchingof the cap to the dimensions of E and T (see FIG. 1), ensuring a secureseal when the cap 200 is completely closed.

The cap 200 comprises a neck seal 220, in the form of a liner around thelid 206. In use, the cap 200 is fully tightened so that the mouth of thebottle 218 is completely sealed against the neck seal 220.

FIG. 3 shows a cross-sectional representation of the screw cap 200according to an embodiment of the present invention, zoomed in on thethreads 208, 102. The attachment portion 212 has a reduced thicknessrelative to the rest of the female thread 208 and acts like a hinge,allowing the thread 208 to deflect when in engagement with the malethread 102. The thickness of the narrow region is approximately 70% ofthe thickness of the rest of the female thread 208.

FIG. 4 shows a detail of the cross-section of the female thread of thescrew cap 200, with typical dimensions in millimetres for an examplethread. It will be appreciated that these dimensions are shown forillustrative purposes only. Screw caps of different sizes, formed ofdifferent materials, or suitable for different applications, may havedimensions that vary considerably from those shown. As shown, the thread208 extends at an angle from the inner surface of the outer wall 204 toa distance (total length, C) of 6.0 mm. The main portion 214 has asubstantially uniform thickness (A) of 1.25 mm. The attachment portion212 has a thickness (B) of 0.87 mm (a reduction in thickness of about30% compared to the main portion) and extends to a length (D) of 0.8 mm(about 13% of the total length of the female thread). The end portion216 has a length (E) of 1.8 mm (about 30% of the total length of thefemale thread). Also as shown, 0.5 mm radius fillets are provided wherethe thread 214 joins the inner surface of the outer wall 204, as well asother radiuses on the outer form of the thread 208.

1. A screw cap for sealing a container with a threaded neck, the screwcap comprising: an outer body, comprising: a cylindrical outer wallclosed at one end by a circular lid, and an interior neck seal adjacentto the circular lid; and a female thread extending around an innersurface of the cylindrical outer wall, the female thread comprising: amain portion having substantially uniform thickness, and an attachmentportion having a thickness which is less than the thickness of the mainportion; wherein the female thread is attached to the inner surface ofthe cylindrical outer wall in the region of the attachment portion, andwherein the attachment portion is configured to permit deflection of thefemale thread.
 2. The screw cap according to claim 1, formed of amoulded polymer material.
 3. The screw cap according to claim 2, whereinthe moulded polymer material is selected from one or more of the groupconsisting of: HDPE, LDPE, polyamide or polyacetal.
 4. The screw capaccording to claim 1, wherein the thickness of the attachment portion isbetween 90% and 50%, between 80% and 60%, or more preferably between 75%and 67% of the thickness of the main portion.
 5. The screw cap accordingto claim 1, wherein the attachment portion has a length that is morethan 5% and no more than 33%, more than 5% and no more than 20%, orbetween 10% and 15% of a total length of the female thread.
 6. The screwcap according to claim 1, wherein the main portion comprises an inclinedregion that extends from the attachment portion in a direction away fromthe lid of the outer body.
 7. The screw cap according to claim 6,wherein the inclined region extends from the attachment portion at anangle of between 10° and 65°, between 20° and 55° or between 30° and45°.
 8. The screw cap according to claim 7, wherein the main portionfurther comprises an end portion which extends from the inclined regionat an angle, such that the end portion is substantially parallel to thelid of the outer body.
 9. The screw cap according to claim 8, whereinthe end portion has a length that is between 10% and 40%, or between 25%and 33% of the total length of the female thread.